1. Field of the Invention
The present invention relates to a decoding method, and more particularly relates to a decoding method of an optical storage system that reduces the decoding error rate of channel bits by adjusting radio frequency (RF) values of the optical signal.
2. Description of the Prior Art
Encoding method is a very important part of the digital systems, especially the digital communication systems and data storage systems. Generally there are three types of encoding methods: source coding, error control coding, and channel coding. The object of source coding is to transform the information from human or computer to the sequence of digital data, especially binary sequence, and compress contents of the information. The object of error control coding is to encode the sequence of digital data becoming a new sequence of bits with functions of error signal detection and correction. And the object of channel coding is to modify the sequence of bits into communication channel or storage media that transfer or store the data more conveniently and reliably.
The Run-Length Limited (RLL) code is commonly used in the encoding of channel bits upon disc storage devices, such as hard disk, CD-ROM, DVD-ROM. The RLL code is usually represented as RLL(m,n) which means that the number of “0”s between two “1”s is at most n and at least m in the data encoded in the Non-Return-to-Zero (NRZ) rule. For example, there are at most seven “0”s and at least one “0”, between two “1”s in the codeword encoded with RLL(1,7).
The data retrieve process in an optical storage system is described below. The pick-up head emits a laser beam to the disc, and the pick-up head then receives the reflection of the laser beam and retrieves the RF values of channel bits by using the partial response maximum likelihood (PRML) detection to recover the recorded data of channel bits. Thereafter, the data of channel bits is decoded by using the error control code to retrieve the data bits. Because of the noise and jitter, the RF values of the detected channel bits usually diverge from the level of the ideal RF values. Thus the decoding results of the back-end channel bits may be affected by the divergence of the RF values.
The error control/correction code is not good enough to reduce the overall data error rate of the optical disc system; especially the current trend is towards increasing the storage density of the discs. The object of the present invention is to provide a decoding method that improves the overall decoding efficiency by reducing the error rate of channel bits.